The invention relates generally to measuring apparatus and more specifically concerns apparatus located at ground level for measuring the speed and height of an aircraft.
Noise pollution from aircraft is becoming more and more of a problem. In order to come up with solutions to this problem it is necessary to make many measurements of the noise generated by the aircraft that are in present use. Typically, to make measurements of the noise generated by an aircraft, an array of microphones is placed along and on both sides of the aircraft's expected path of travel as projected on the ground. Then the distance from the noise source (aircraft) to the ground-based microphones must be determined so that the sound pressure measurements can be corrected for propagation losses. To determine the distance from the noise source to the microphones, it is necessary to know the aircraft's speed and height above the ground as it travels along its expected path. Once the aircraft's height and speed at some known point relative to this array is determined, the distance from each microphone to the aircraft can be calculated for each data point. It is, therefore, the primary purpose of this invention to provide apparatus that is simple and inexpensive for measuring the speed and height of an aircraft as it travels along its expected path.
Prior apparatus for measuring aircraft height and ground speed used an aircraft radar altimeter on the ground in an upside down configuration. The disadvantages of the radar altimeter apparatus are the acquisition times are excessive and the zenith crossing times cannot be measured with sufficient accuracy, resulting in corresponding errors in determining aircraft speed. It is, therefore, an object of this invention to provide apparatus for measuring the height and speed of an aircraft that decreases the disadvantages that have been encountered with previous apparatus.